The Mandaeans have Hiwil Ziwa (= Jesus) baptizing Jesus as the start of their religion:

This is the "loosing" (consecration) of incense for baptism.]

[In the name of the Great Life! May my thought, knowledge and understanding be enlightened, mine, Adam-Yuhana son of Mahnush, by means of these (prayers), admonitions and hymns of baptism, which were transcribed from the scroll The Great Wellspring. This is the baptism wherewith Adam the first man was baptised by Hibil-Ziwa when he breathed the pure mana into him and he got up, sneezed and lived.

And Adam questioned, and spoke, "Through the power of Hibil-Ziwa have I attained my end!"

Then Hibil-Ziwa arose, put on the seven vestments, and went to the jordan-bank. When Adam had placed the qauqa (and) fire before Hibil-Ziwa, Hibil-Ziwa twined a wreath for his staff and twined a wreath for Adam, then rose and went to the jordan and recited the prayer "Answer me, my father, answer me, for I have gone to the jordan in the strength of my father Yawar, and in the strength of Manda-d-Hiia a wreath hath been set upon the 'uthras."

Then he arose and recited "In the name of that First Being" for his crown and set it on his head, then recited "Life created Yawar-Ziwa", "Let there be light" and Manda created me" for the myrtle-wreath and set it beside the crown.

And he held the end of his stole and recited "Strengthened and enhanced is the great mystery of radiance, light and glory" over his pandama, folded his pandama over his mouth and recited "incense that is fragrant, yea, for the First Life" and cast incense on the fire. And he recited "We have acknowledged," "Praises", "Thee, Thyself", "I sought to lift mine eyes", "The day that the jordan was bestowed on Sam-Smir", "I have worshipped and praised that Yawar-Ziwa" and "I am Yur son of Barit; in great radiance". And he held his stole and recited "I went to the jordan, but not I alone" up to the place where it says "give free movement to the limbs of my body; I go down," and he went down into the jordan up to a fourth of his thighs. And he recited "In the name of Yusmir, the First Vine" over his staff, and at the place where it saith "covered with radiance and clothed in light" he cast the myrtle-wreath over the staff and "clothed" it with his stole.

And he recited "Bound is the sea" and traced three circles thrice over in the jordan. And he recited "I am a perfected gem", and "Avaunt, flee in fear" and splashed the water in the jordan at his right, his left and in front of him and recited "Piriawis" as written. Then he chanted a hymn and said to him "Any man who hath strength thereto and who loveth his soul, let him come and go down to the jordan, be baptised, receive the pure sign, put on robes of radiant light and set a fresh wreath on his head."

And Adam descended into the jordan and submerged himself thrice behind him (Hibil-Ziwa), who took him by the right hand transferred him to his left, placed him between himself and his staff, dipped him thrice and signed him thrice in the jordan.

And he gave him three palmfuls of water to drink and recited "Manda created me" over the myrtle-wreath and set it upon his (Adam's) head and pronounced the secret names over him.

(Then) he took his hand in kushta over the staff and made him go up before him.

(Then) he took water from the jordan into his phial and recited the hymn "At the waterhead I went forth" and "Blessed art thou, Outer Door", and recited "I rose up from the jordan, and a group (of souls) I met". And he came up out of the jordan and completed it (the hymn). And he took up the oil and recited "We have acknowledged the name of Life", "Precious oil art thou" and "Thou wast established, First Life" over the oil. Then he signed him thrice and made passes over him thrice, and at each signing he laid his hand on his (Adam's) head and repeated those names which he had pronounced over him in the jordan.

And he performed kushta with him. (Then) he took the pihta and recited the eight prayers for the pihta over the pihta and the two prayers for the mambuha over the mambuha. And he gave him the pihta so that he should eat and gave him the mambuha that he might drink, and he drank the rinsing (water).

And he grasped his hand in kushta and seated him before him and recited the "sealing" prayers, "When a jordan of living water and bestowed upon Sam-Smir, the great Radiance of Life", "Bound and sealed", "By 'Usar-Hiia" and the greater (longer) "Bound and sealed" and laid his hand upon him and stood and recited "Ye are set up and raised up", "What did thy Father do for thee, Soul?", "How lovely are the plants which the jordan planted and raised up", "Rightly did my baptiser baptise me", "Shilmai baptised me with his baptism and Nidbai", "The jordan in which we were baptise will bear us witness", and "I rejoice in my priests and Nasoraeans who hearken to my converse".

And he chanted the hymns "Truly do I say to you", "To you I cry and explain" and "A new disciple am I who hath come to the jordan bank".

And he read all the hymns and homilies unto their end and recited "Blessed and praised be Life" of Shum son of Noah and "Good is the good for the good". And he recited "In radiance that is great am I immersed" and loosed his kanzala (stole) and "honoured" his crown.

And Life is victorious.]

“Finally, from so little sleeping and so much reading, his brain dried up and he went completely out of his mind.”
― Miguel de Cervantes Saavedra, Don Quixote

Here I found the transcription of the fragment (albeit undoubtedly more could be retrieved I think because of advances in technology). My guess (owing to the apparent style) is that it was written by Ephrem (cf Harnack too https://books.google.com/books?id=VOI-A ... 2C&f=false):

"Marcion ... said that our Lord was not born of woman, but stole the place of the Creator and came down and appeared first between Jerusalem and Jericho, like a Son of Man in form and in image and in likeness, yet without our body. And he in no wise brings the history of the Blessed Mary into his teaching, and does not confess that he received a body from her and appeared in flesh, as the Holy Scriptures teach. But Mani declares the body of the family of Adam to be wholly polluted, and says that the body is of the evil essences, and of darkness and of the Serpent. In like manner did Bardaisan reckon the body to be of hyle, and to have been created of the dregs of wickedness, and to be polluted, and to have no resurrection. And the Spirit, the Paraclete, considering these very teachings of the heretics who reject the human body which was created in the image and likeness of God, declared beforehand these things by means of the divine writings of Matthew and Luke, viz., the public genealogy of the Christ and his birth in flesh, which was derived from David and from Abraham who were of the race of the family of Adam.

. . in the Scriptures of the Gospel the Apostolic voice beginneth by saying plainly that not from angel did, he take, but from the seed of Abraham he took: that these good tidings which come to the children of men might be known openly, viz., that from them the Only One of God received a body. And Adam who was fallen arose, he and this fair image («., the body) which was the cause of all the way of the dispensation of Messiah, as Luke testified in the Scriptures of the genealogies reckoning backwards from Joseph, legally, in that it was necessary, and truly (cimtlth) in that he gave to her a true hand [in marriage]. And he confirmed the writing (machtvānāth) of Matthew, which was (dahváth) among the Hebrews, declaring that the Christ was born of David and Abraham according to the plighted promise [deposited] with them. And he carried back his reckoning to Adam, who was the image of God and the likeness of the form of His son, And he [Adam] was the drachm that was lost by the Godhead in the dark world. And [the Godhead] sought and found it by the light of the Word which came to be revealed in the flesh, as it is written, Thy word is a lamp to my feet and a light tomy paths. For He is the Son, the Word, the Lamp, the Light, and by His revelation he gave light to Adam, who was dark by reason of his transgression of the commandments, as it is said, The Lord my God shall lighten my darkness.

“Finally, from so little sleeping and so much reading, his brain dried up and he went completely out of his mind.”
― Miguel de Cervantes Saavedra, Don Quixote

The subject seems to confirm that (a) the Marcionites were originally connecting Adam with this descent between Jerusalem and Jericho and then (b) additional details about the Manichaean tradition about Adam are provided. I will write Sebastian Brock to have this material re-examined in light of modern infrared technology which might reveal more (or maybe not given the fragmentary nature).

“Finally, from so little sleeping and so much reading, his brain dried up and he went completely out of his mind.”
― Miguel de Cervantes Saavedra, Don Quixote

An interesting clue about knowledge of the lost Marcionite gospel. Jesus coming to Adam and recreating him is hinted in Pauline theology. It becomes very explicit in the Alexandrian tradition especially Clement - even though he rarely makes mention of Adam in his writings. A passage from the Stromata is especially relevant. It happens to be a citation of Barnabas which reads:

Forasmuch then as He was about to be manifested in the flesh and to suffer, His suffering was manifested beforehand. For the prophet saith concerning Israel; Woe unto their soul, for they have counseled evil counsel against themselves saying, Let us bind the righteous one (Δήσωμεν τὸν δίκαιον), for he is unprofitable for us. What sayeth the other prophet Moses unto them? Behold, these things saith the Lord God; enter into the good land which the Lord swear unto Abraham, Isaac, and Jacob, and inherit it, a land flowing with milk and honey. But what saith knowledge? Understand ye. Set your hope on Him who is about to be manifested to you in the flesh, even Jesus. For man is earth suffering; for from the face of the earth came the creation of Adam. What then saith He? Into the good land, a land flowing with milk and honey. Blessed is our Lord, brethren, who established among us wisdom and understanding of His secret things. For the prophet speaketh a parable concerning the Lord. Who shall comprehend, save he that is wise and prudent and that loveth his Lord?

Forasmuch then as He renewed us in the remission of sins, He made us to be a new type, so that we should have the soul of children, as if He were recreating us. For the scripture saith concerning us, how He saith to the Son; Let us make man after our image and after our likeness, and let them
rule over the beasts of the earth and the fowls of the heaven and the fishes of the sea. And the Lord said when He saw the fair creation of us men; Increase and multiply and fill the earth. These words refer to the Son. Again I will shew thee how the Lord speaketh concerning us. He made a second creation at the last; and the Lord saith; Behold I make the last things as the first. In reference to this then the prophet preached; Enter into a land flowing with milk and honey, and be lords over it.

Behold then we have been created anew, as He saith again in another prophet; Behold, saith the Lord, I will take out from these, that is to say, from those whom the Spirit of the Lord foresaw, their stony hearts, and will put into them hearts of flesh; for He Himself was to be manifested in the flesh and to dwell in us. For a holy temple unto the Lord, my brethren, is the abode of our heart. For the Lord saith again; For wherein shall I appear unto the Lord my God and be glorified? I will make confession unto Thee in the assembly of my brethren, and I will sing unto Thee in the midst of the assembly of the saints. We therefore are they whom He brought into the good land.

What then is the milk and the honey Because the child is first kept alive by honey, and then by milk. So in like manner we also, being kept alive by our faith in the promise and by the word, shall live and be lords of the earth. Now we have already said above; And let them increase and multiply
and rule over the fishes. But who is he that is able [now] to rule over beasts and fishes and fowls of the heaven; for we ought to perceive that to rule implieth power, so that one should give orders and have dominion. If then this cometh not to pass now, assuredly He spake to us for the hereafter, when we ourselves shall be made perfect so that we may become heirs of the covenant of the Lord.